Japanese Patent Application Publication No. 2013-468549 discloses a semiconductor device including a diode. This semiconductor device has a semiconductor substrate, a front surface electrode, and a rear surface electrode. The front surface electrode covers substantially a center portion of a front surface of the semiconductor substrate. The rear surface electrode covers an entire range of a rear surface of the semiconductor substrate. The diode is formed in a region (hereafter, “element region”) of the semiconductor substrate interposed between the front surface electrode and the rear surface electrode. Upon when the diode turns on, current flows from the front surface electrode toward the rear surface electrode. The semiconductor substrate includes an outer circumferential voltage withstanding region around the element region (i.e., between the element region and an outer circumferential end surface of the semiconductor substrate). The outer circumferential voltage withstanding region includes a plurality of p-type guard rings and an n-type outer circumferential drift region. The guard rings are exposed on the front surface of the semiconductor substrate and surround the element region in layers of rings therearound. The outer circumferential drift region separates the guard rings from each other. When the diode has turned off, a potential difference is generated in a lateral direction (direction from an inner circumferential side to an outer circumferential side) in the outer circumferential voltage withstanding region. Then a depletion layer extends from the element region to the outer circumferential drift region. When the depletion layer reaches the guard ring on an innermost side, the depletion layer further extends from that guard ring toward the outer circumferential side. When the depletion layer reaches the second guard ring from the inner circumferential side, the depletion layer further extends from that second guard ring toward the outer circumferential side. As above, the depletion layer extends to the outer circumferential side by way of the respective guard rings. That is, the plurality of guard rings enhances the extension of the depletion layer toward the outer circumferential side in the outer circumferential voltage withstanding region. Due to this, the depletion layer extends broadly in the outer circumferential voltage withstanding region, and reduces electric field in the outer circumferential voltage withstanding region. It should be noted that although the diode is provided in the element region in Japanese Patent Application Publication No. 2013-468549, even when another type of semiconductor element (e.g., MOSFET (abbreviation of Metal-Oxide Semiconductor Field-Effect Transistor) or IGBT (abbreviation of Insulated Gate Bipolar Transistor)) is provided in the element region, the electric field in the outer circumferential voltage withstanding region can be reduced by the guard rings.